Method and apparatus for the presentation of three-dimensional images

ABSTRACT

There is disclosed a method and apparatus for the presentation of three-dimensional images, where light beams with appropriate intensity and optionally with appropriate color are projected in different viewing directions and thereby creating a three-dimensional image. The light beams are created with a light emitting surface ( 10 ) comprising cyclically addressable light sources (S). The surface ( 10 ) is positioned behind a screen ( 20 ) comprising pixels (P) with a controllable light transmission or reflection. The light beams emitted from different light sources (S) illuminate the individual pixels (P) from different directions. According to the invention, the distance between the light sources (S) is larger than the distance between the pixels (P), and the light sources (S) are positioned so much away from the pixels so that the number of pixels (P) illuminated by one light source (S) is greater than the number of light sources illuminating one pixel (P).

TECHNICAL FIELD

[0001] The invention relates to a method and apparatus for thepresentation of three-dimensional images, particularly for moving(video) images. The invention is applicable in all areas of imagedisplaying.

BACKGROUND ART

[0002] If a plane—two-dimensional—image is displayed on a surface, thenevery point of the surface emits or reflects light with approximatelysame intensity (and color) in all directions. This is the workingprinciple of a traditional picture, like a postcard (reflection) or atraditional TV-image (light emission). In the case when athree-dimensional image is presented, the emitted light has a differentintensity (and color) in the different directions, even if it is emittedfrom the same point. We may regard in this way a window pane or ahologram as a display. Hence, in order to display a three-dimensionalimage, there is needed a light emitting surface where the intensity (andcolor) of the light emitted from a single image point (pixel) may becontrolled as the function of the emission angle (exit angle), withother words, the intensity of the light emitted in the differentdirections may be controlled.

[0003] With some of the known systems suitable for displaying spatial(stereoscopic) images, two images are projected, which may be separatedfrom each other by colour filters, polarising filters, or bytime-sequentially driven eyeglasses. These effect of the separatedimages are perceived as three-dimensional, when the two images aresensed by the left and right eye, respectively. These images are nottrue three-dimensional images, because they only provide the same twoperspectives, independent of the position of the viewer in relation tothe image. There are other known devices, called autostereoscopicdevices, which permit the viewing of stereo images also without aidingmeans. Such a stereoscopic display is disclosed in EP 0 721 132 and EP 0729 055, among others.

[0004] In order to produce true or realistic three-dimensional images, alarge number of light beams must be projected in the differentdirections in space, with the appropriate intensity/colour, which allowthe viewer to see different perspectives from different viewpoints. Insome of the prior art displays, two surfaces are used for displayingrealistic three-dimensional images. The first front surface is a surfacewith a controllable light transmission or reflection, and the secondback surface is an illuminating surface comprising light sources. Onepoint of the back surface and one point of the front surface definesunequivocally a direction. With a possible embodiment, the image iscreated on the back surface by controlling the intensity and/or colourof the light sources, while on the first surface only masking isperformed according to the selected viewing directions, by switching theimage pixels on and off. With an other possible embodiment, the lightsources on the back surface are continuously on, or they are onlyswitched on or off, while the controlling according to the imageinformation is made on the first surface. The first surface comprisingthe image pixels with controllable light transmission or reflection ispreferably an LCD display.

[0005] Such solutions utilising an LCD display are disclosed, amongothers, in the documents U.S. Pat. Nos. 5,831,765, 5,036,385, WO99/07161, EP 0 316 465 and U.S. Pat. No. 5,132,839. In these knownsolutions, illuminated strips are used behind an LCD screen, and thelight of the strips are either transmitted or blocked by the controlledimage pixels of the LCD screen.

[0006] In the solution disclosed in EP 0 316 465, there is anilluminated line behind every pair of LCD-pixel columns, and the lightof the line passes through either one column or the other, correspondingto the control of the LCD pixels. This arrangement allows the display ofa stereoscopic image with two viewing directions, but the resolution ofthe LCD-display is low, because two LCD-pixels are needed for an imagepoint. The description suggest to increase the number of LCD-pixelsassociated to one illuminating line, in order to increase the number ofviewing directions, but this leads to a further lowering of theresolution.

[0007] With an other possible embodiment, it is suggested to use oneilluminating line (light source) behind each LCD-pixel column. In thiscase every pixel is illuminated by multiple light sources, which resultsin several viewing directions, having independently controllable lightemissions in the same image point. Such a display is described in thepublication “A prototype flat panel hologram-like display that producesmultiple perspective views at full resolution”, by J. Eichenlaub, in:Proceedings of the SPIE Vol. 2409, pp. 102-112. The principle of thisknown solution is shown in FIG. 1. Here, the number of the light sourcesis essentially equal to the number of the image pixels in a row.Therefore, in order to produce an image with an acceptable resolution, alarge number of very small light sources are needed. These light sourcesare extremely expensive, due to their small size and the large quantityneeded. The light sources may be manufactured by optical methods (e. g.cylindrical lens matrix, disclosed in WO 94/06249), but this requiresagain a very precise and costly technology, and the illumination angleis also limited. A further disadvantage of this approach is the limitedintensity which may be achieved. A similar method is disclosed in U.S.Pat. No. 5,036,385., but only for use as a stereoscopic display, i. e.with only two different views for the left and right eyes for theobserver.

[0008] U.S. Pat. No. 5,132,839 teaches a solution where an appropriateoptical system positioned between the illuminating surface and the LCDscreen produces light beams in different directions, but parallel toeach other. With this system the LCD-screen is illuminated periodicallyin different directions, and the LCD-screen is controlled such that theimage corresponding to the actually illuminated direction should appearon the on the LCD-screen in the corresponding moment. This solution alsorequires the use of small light sources, which results in the lowintensity, as mentioned above. Also, the optical system (Fresnel lens,lens matrix) for the parallel illumination of the LCD displays makes thedevice expensive and complicated.

[0009] Accordingly, it is an object of the invention to provide a methodand apparatus for the presentation of realistic three-dimensionalimages, preferably for moving images, which allows the display of theimages without aiding means and without spatial limitations, and whichfurther do not need expensive focusing and deflecting optical elements.

SUMMARY OF THE INVENTION

[0010] According to a first aspect of the invention, there is provided amethod for the presentation of three-dimensional images. In the methodlight beams with appropriate intensity and optionally with appropriatecolour are projected in different viewing directions, thereby creating athree-dimensional image.

[0011] In the proposed method a light emitting surface comprisingseparately controllable light sources with angle independent ortime-constant angle dependent radiation characteristics is positionedbehind a screen, the screen comprising image pixels with a controllablelight transmission or reflection. The light beams emitted from differentlight sources illuminate the individual image pixels from differentdirections, and further the direction of the light beams emitted fromthe individual image pixels are determined by the direction of the lightbeams that are emitted by the light sources and propagating between thelight sources and the image pixels substantially without changingdirection. According to the method, the distance between the lightsources are selected larger than the distance between the image pixels,and the light sources are positioned so much away from the image pixelsso that the number of image pixels illuminated by one light source isgreater than the number of light sources illuminating one image pixel.

[0012] The suggested arrangement results in a number of advantages.Firstly, light sources with a larger size may be used. Secondly, arelatively small number of light sources is necessary.

[0013] The angle dependent radiation characteristics is advantageouslyset to spread light beams into the valid field of view (FOV), in orderto maximise brightness and minimise side effects beyond the FOV. Thevalid field of view is where the viewer can see true three-dimensionalimage, defined by the angle between the two farthest pixels illuminatedby one light source.

[0014] The distance between the light sources is understood as thedistance between the centres of the light sources, if the light sourcescan not be regarded as point-sources. Also, the distance between theimage pixels is meant to be the distance between the centres of theimage pixels, because the image pixels can normally not be regarded aspoint objects.

[0015] According to an especially preferred realisation of the method,the ratio of the number of image pixels illuminated by one light sourceto the number of light sources illuminating an image pixel equals theratio of the distance between the centres of the light sources to thedistance between the centres of the image pixels. Thereby fewer andlarger light sources are sufficient to produce an image with the sameresolution.

[0016] In order to see a three-dimensional image with a continuous lightintensity and without flickering, according to a further aspect of theinvention, it is suggested that the light beams emitted from theindividual image pixels are spread in horizontal and vertical directionwith a divergence angle necessary for the uniform illumination of athree-dimensional image, where the horizontal divergence angle is atleast as large as the angle between two neighbouring viewing directions,and, as practice has shown, it is not more than twice of the anglebetween two neighbouring viewing directions. In this case the viewerwill perceive a continuous image, independent of the angle in whichhe/she is looking at the screen.

[0017] It is also preferred that for a true three-dimensional image bothvertically and horizontally the image pixels are illuminated by lightsources which are adjacent to each other and have uniform surfaceillumination, and the size of which is essentially determined by thehorizontal and vertical distance between them.

[0018] In case the vertical parallax information is omitted, thedifferent horizontal and vertical spread of the lights emitted from theimage pixels may be obtained by adjacent vertical light source strips.

[0019] With an other preferred embodiment, point-like light sources areused, and the different vertical and horizontal spread (divergence) ofthe light beams emitted from the individual image pixels are achievedwith an appropriate diffuser, e. g. with a holographic of lenticularlens diffiser.

[0020] In the most preferred embodiment, the images displayed with themethod are obtained by modulating the image pixels on the screen withthe image information. In this case it is foreseen that the image pixelsand the light sources are controlled in a manner that

[0021] a, the light sources are switched on and off individually or ingroups so that an image pixel is illuminated at one time by not morethan one light source, and at the same time each image pixel isilluminated by a light source,

[0022] b, the light sources are switched on and off periodically orcyclically one after the other so that in each period or cycle eachimage pixel is illuminated at least once in each viewing direction, andin the meanwhile

[0023] c, the images projected in the different directions are obtainedby the appropriate intensity and/or colour modulation of the lighttransmitted through or reflected from the image pixels,

[0024] In this case, groups are created from the illuminating lightsources, where as many neighbouring light sources constitute a group asthere are viewing directions. The switching of the light sources areperformed in a manner so that at one time only one light source isswitched on from each group, preferably the light sources in the similarposition within the groups, while those image pixels of the lightemitting screen comprising the controllable image pixels, whichcorrespond to a selected viewing direction—in case of athree-dimensional image without vertical parallax information, thecolumns of pixels—are controlled with the appropriate image informationcorresponding to the selected viewing direction. After this, the lightsources currently on are switched off substantially simultaneously ineach group as the light sources in the next position are switched on,and simultaneously the control of the controllable image pixels ischanged corresponding to the next viewing direction. It is emphasisedthat the resolution of the LCD-screen will not decrease, but thecontrolling frequency will increase proportionally with the number ofthe viewing directions.

[0025] It is suggested that the control of the light sources and theimage pixels are repeated periodically, where one period is not longerthan 1/20 s, preferably 1/25 s. Within one control cycle each lightsource is activated once, while within one control cycle each imagepixel is controlled once in each viewing directions, that is within onecontrol cycle as many times as there are viewing directions. Thisarrangement ensures that the still and video images will be perceivedsubstantially free of flickering.

[0026] However, it is also possible to obtain the three-dimensionalimages by modulating the light sources with the image information, andusing the pixels on the screen only to select the appropriate viewingdirections to the modulated light sources. In this case the image pixelsare realised as light shutter pixels, and a composed image containingparts of a complete image is generated on the light emitting surface bymodulating the light intensity emitted by the light sources. Further,the shutter pixels and the light sources are controlled in a manner that

[0027] a, a single shutter pixel is illuminated at one time by a groupof light sources, each of the light sources in that group correspondingto a viewing direction, and at the same time the light of one lightsource within that group being transmitted through a single shutterpixel only,

[0028] b, the shutter pixels and the light sources are modulated so thatin each image cycle each shutter pixel is transmitting or reflectinglight at least once in each viewing direction, and

[0029] c, the complete images projected in the different directions areobtained by cyclically transmitting light through the shutter pixels.

[0030] According to an other aspect of the invention, there is alsosuggested an apparatus for the presentation of three-dimensional images,particularly for the performing of the method according to theinvention.

[0031] The apparatus of the invention comprises a light emitting surfaceprovided with separately controllable light sources with angleindependent or time-constant angle dependent radiation characteristics,and a screen comprising image pixels with a controllable lighttransmission or reflection and positioned before the light emittingsurface. In the apparatus the light of the light sources propagatesessentially without changing direction between the light sources and theimage pixels, and through the image pixels or the light of the lightsources is reflected from the image pixels. The light sources and theimage pixels are arranged so that each light source illuminates severalimage pixels, and one image pixel is illuminated by several lightsources,

[0032] According to the invention, the distance between the centres ofthe light sources is larger than the distance between the centres of theimage pixels, and the distance between the light sources and the imagepixels is selected so that more image pixels are illuminated by onelight source as there are light sources illuminating a single imagepixel.

[0033] As indicated above, the distance between the light sources isunderstood as the distance between the centres of the light sources, ifthe light sources can not be regarded as point-sources. Also, thedistance between the image pixels is meant to be the distance betweenthe centres of the image pixels, because the image pixels can normallynot be regarded as point objects.

[0034] With the most preferred embodiment of the apparatus according tothe invention, the light sources on the back light emitting surface areso far from the image pixels, so that the ratio of the number of pixelsilluminated by one light source to the number of the light sourcesilluminating a single pixel is substantially equal to the ratio of thedistance between the light sources to the distance between the imagepixels. With this arrangement, the number of the light sources may bereduced substantially, without having to sacrifice the angle resolutionof the three-dimensional image.

[0035] In a preferred embodiment, the light emitting surface is a LED orOLED (Organic Light Emitting Diode) screen comprising light sources i.e.R,G,B LED-s. Image can be generated by the continuous grey-scale controlof the image pixels on the screen or by control of each LED. These maybe of different colours. The transmission or reflection of the properimage pixels of the screen, preferably an LCD display, may also becontrolled between on and off states only.

[0036] If it is desired to display true three-dimensional images thatare realistic both vertically and horizontally, then it is suggestedthat the light sources are formed as light sources with a predeterminedvertical and horizontal size in order to provide means for spreading ofthe light beams emitted from the individual image pixels in vertical andhorizontal directions, to ensure the uniform illumination of thethree-dimensional image.

[0037] If it is sufficient to display images without the verticalparallax information, then the light sources are formed as verticallight source strips positioned adjacent to each, in order to providedifferent spread of the light beams emitted from the individual imagepixels in vertical and horizontal directions.

[0038] However, if it is chosen to use light sources which aresubstantially point sources, than it is suggested that the screencomprising the controllable image pixels comprises a diffuser, like aholographic or lenticular lens matrix in order to provide differentspread (divergence) of the light beams emitted from the individual imagepixels in vertical and horizontal directions.

[0039] It is also feasible that there are multiple light sources at anequal distance below each other behind the diffusing surface. In orderto display colour images, it is suggested that the light sourcespositioned below each other are light sources for the irradiation ofbasic colours suitable for the presentation of coloured images, andwhere the basic colours are repeated regularly.

BRIEF DESCRIPTION OF DRAWINGS

[0040] The invention will be now described more in detail with referenceto the non-limiting embodiments illustrated in the accompanyingdrawings, where

[0041]FIG. 1 is a top view of a prior art display arrangement,

[0042]FIG. 2 is a schematic top view of a display arrangement accordingto the invention,

[0043]FIG. 3 is a schematic cross-sectional view of a first solution toachieve horizontal spread (divergence) of the light beams,

[0044]FIG. 4. is a schematic cross-sectional view of a second solutionto achieve horizontal spread (divergence) of the light beams,

[0045]FIG. 5 is a top view of a first embodiment of the illuminatingstrips used in the apparatus of the invention,

[0046]FIG. 6 is a top view of a second embodiment of the illuminatingstrips used in the apparatus of the invention,

[0047]FIG. 7 is a front view of a part of the one-coloured illuminatingstrips,

[0048]FIG. 8 is a time-diagram of the controlling of the one-colouredstrips,

[0049]FIG. 9. is a front view of a part of the three-colouredilluminating strips,

[0050]FIG. 10 is a time-diagram of the controlling of the three-colouredstrips,

[0051]FIG. 11 is a top view of a schematic display arrangement showingthe light sources at maximal distance to the screen,

[0052]FIG. 12 is a top view of a schematic display arrangement showingthe light sources at half of the maximal distance to the screen,

[0053]FIG. 13 is a top view of a schematic display arrangement showingthe light sources at a quarter of the maximal distance to the screen,

[0054]FIG. 14 is a schematic perspective view of a first displayarrangement used in the apparatus according to invention,

[0055]FIG. 15 is a schematic perspective view of a second displayarrangement used in the apparatus according to invention,

[0056]FIG. 16 is a schematic perspective view of a third displayarrangement used in the apparatus according to invention.

[0057]FIG. 17 is a schematic top view of a display arrangement ofanother embodiment, similar to that shown in FIG. 2, but in reflectiveconfiguration, and

[0058]FIG. 18 is a side view of the arrangement shown in FIG. 17, and

[0059]FIG. 19 is a schematic perspective view of another embodiment ofthe apparatus embodying the inventive concept,

[0060]FIG. 20 is a schematic figure illustrating the geometricalarrangement of the light emitting surface and the shutter pixels in thesecond embodiment of the apparatus,

[0061] FIGS. 21A-21E illustrate the control cycle of the light sourcesand the shutter pixels within an image frame, and

[0062]FIG. 22 is a schematic figure of the radiation characteristic of aLED used in the light emitting surface in the second embodiment of theapparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

[0063] In the display arrangement shown in FIG. 2, there is provided ascreen 20 having controllable light transmission properties, positionedbefore a light emitting surface 10.

[0064] It will be shown with reference to FIGS. 17 and 18 that thescreen 20 may be screen where the reflection of the pixels may becontrolled. For easier illustration and understanding of the inventiveconcept, the principle will be explained with the help of a transmissivescreen 20.

[0065] The screen 20 may be embodied by an LCD display, having imagepixels P. The centres of the image pixels P are at equal distances Xp toeach other. The 10 light emitting surface is at a distance D2 to thescreen 20, and there are light sources S1 . . . Sn on the light emittingsurface 10, where the light sources S1 . . . Sn are in a distance Xsform each other. The distances Xs are also measured between the centresof the light sources S1 . . . Sn. The light sources may be controlledseparately from each other, but, as will be shown below, some of themmay be actually controlled (modulated) simultaneously. Theoretically,separate light sources S may be positioned behind every image pixel P,and thus a true or realistic three-dimensional (3D) image may bedisplayed, which shows 3D effect both vertically and horizontally.However, such an arrangement would require the processing, storage,transfer and display of very large amounts of information, which can notbe economically realised at present. Due to the structure of the humaneye and the way we perceive 3D images, it is sufficient if the differentvertical views are omitted. In this case it is sufficient to realise thelight sources as illuminating vertical lines or strips. Because nodeflecting optical elements are used between the light emitting surface10 and the screen 20, the exit angle β of the light sources S is equalto the viewing angle α of the screen 20, that is α=β. The relationbetween the exit angle β, the viewing angle α, the distance D, thedistance Xp and Xs may be described as follows:

tan (β/2)=tan (α/2)=Is·Xp/2D=Ip·Xs/2D,

[0066] where following denotation is used:

[0067] β exit angle (range)

[0068] α view angle (range)

[0069] Ip the number of the independent viewing directions, also thenumber of light sources S illuminating one pixel P

[0070] Is the number of pixels P which are illuminated by one lightsource S

[0071] Xp the distance between the centres of neighbouring pixels P

[0072] Xs the distance between the centres of neighbouring light sourcesS

[0073] D the distance between the screen 20 and the light emittingsurface 10.

[0074] The viewing angle α is defined as the largest angle between thelight beams exiting from a pixel P. Good quality 3D images and a largefield of view may be achieved with a viewing angle α of 60°. Of course,the viewing angle α may be larger as well.

[0075] As an example, selecting α=60°, the distance D between the lightemitting surface 10 and the screen 20 may be calculated as D=Is·Xp·tan(60°/2)=Is·Xp·{square root}3. This value of the distance D is defined asthe basic distance.

[0076] Turning to the value of Is, it is advisable to select the numberof the viewing directions in a manner so that the angle γ between twoneighbouring viewing directions does not exceed 2°. This angle betweenthe viewing directions (with other words, the angle resolution) isdefined as the angle γ between two light beams, which are emitted fromthe centres of two neighbouring light sources, and are propagatingthrough a common pixel. Seen from the outside, a viewer will perceivethat the two light beams exit from the pixel as if they were emitted bya common light source within the pixel, but in different directions. Theangle resolution of the display is high, if the value of the angle γ issmall, which enhances the 3D perception of the observer. Obviously,selecting a high number of viewing directions within a fixed viewingangle α will result in a small value of the angle γ.

[0077] Selecting the values α=60° and γ=2°, the number of the viewingdirections will be Ip=60/2=30, which means that each pixel P isilluminated by thirty light sources S, and each light source Silluminates thirty pixels P. This approach is used by the known priorart methods, and it is illustrated schematically in FIG. 1.

[0078] The number of the pixels P should be selected to be in the sameorder of magnitude as with the known displays, i. e. the number of thepixels should be at least 320×240, preferably 640×480, for even betterresolution 800×600, or for higher demands 1024×768. Considering a 12″monitor, with a vertical 320 pixel resolution the distances Xp and Xswill be 0.8 mm, with 640 pixels 0.4 mm, with 800 pixels 0.35 mm, andwith 1024 pixels 0.27 mm. If Xp=Xs, it means that the size of the lightsources are not larger than the size of the pixels. Light sources insuch a minuscule size and in such a large number would mean high costs,and beside, the necessary light intensities are difficult to achieve.

[0079] To overcome this problem, it is suggested to select the distanceXs between the light sources S larger than the distance Xp between theimage pixels P, and it is also suggested to position the light sources Sso much away from the image pixels P, so that the number of image pixelsilluminated by one light source S should be greater than the number oflight sources S illuminating one image pixel.

[0080] As an illustrative example shown in FIG. 2, the light emittingsurface 10 is positioned in a distance D2 that is at least twice thebasic distance D1, which latter is shown in FIG. 1. The relation α=βwill be still valid, because no deflecting elements are applied betweenthe light sources S and the pixels P, but from the relation

tan (β/2)=tan (α/2)=Is·Xp/2D=Ip·Xs/2D,

[0081] it is apparent that the light sources S are twice as far fromeach other as compared to the arrangement shown in FIG. 1, i. e.Xs=2·Xp. While the number of the viewing directions Ip=30 remainsunchanged, the number of the pixels illuminated by one light source willdouble, that is Is=60. In this way, not only the distance between thelight sources doubled, but advantageously the number of the necessarylight sources were reduced as well.

[0082] As it is apparent from the relation Is·Xp=Ip·Xs, in the proposeddisplay the number of the light sources and the number of the lightbeams illuminating different pixels is selected such that their productis equal to the product of the number of pixels and the number of lightsources emitted from a pixel (i. e. the number of viewing directions).This may be also formulated as follows:

Is/Ip=Xs/Xp

[0083] With other words, the ratio of the number of image pixelsilluminated by one light source to the number of light sourcesilluminating an image pixel equals the ratio of the distance between thecentres of the light sources to the distance between the centres of theimage pixels,

[0084] This measure permits the economic manufacture of displays with ahigh resolution, because the pixels defining the resolution of thedisplay may be provided in a large number on the first screen, while thenumber of the viewing directions allowing the 3D effect may be selectedappropriately large as well. However, a relatively small number of lightsources with larger size, or low resolution displays are sufficient onthe second surface, the light emitting surface. It is understood thatthe number N of the light sources will be

N=(n·Ip)+Ip,

[0085] where

[0086] N total number of light sources,

[0087] n=Dmax/D multiplication factor

[0088] Ip the number of viewing directions.

[0089] The maximal distance Dmax is defined as the distance where alight source S with an exit angle β will irradiate or illuminate thetotal width of the screen, or a surface corresponding to the size of thescreen. In that case the central light source, here the light sourceS30, illuminates the screen in an angle β. As it is seen in FIG. 11, inorder to have Ip=30 viewing directions from each pixels, it issufficient to use sixty light sources only, irrespective of the numberof pixels P in a horizontal line on the screen 20. That would also implythat the width of the light emitting surface 10 will be twice the widthof the screen 20. The distance D between the light emitting surface 10and the screen 20 will be {square root}3 times the width of the screen20.

[0090] The increase of the depth of the display apparatus and the widthof the light emitting surface will not always allow this solution,although this still results in a more flat arrangement than the priorart solutions with an intermediate optical system between the lightemitting surface 10 and the screen 20. However, it is more practical tochoose the distance D to be smaller. If D is selected to be Dmax/2, only90 light sources are needed, while Ip remains Ip=30 (see FIG. 12.). Ifthe distance D is halved further, keeping Ip=30 will result in N=150,that is 150 light sources are needed (see FIG. 13). It is apparent fromthe above that the size of the screen and the number of the lightsources may be varied between wide limits by varying the distance D.

[0091] In order to perceive a continuous image by a viewer, it isnecessary that the cones of the light beams passing through theindividual pixels (see FIGS. 15 and 16.) should touch or slightlyoverlap, that is no part of the space within the viewing angle shouldremain partly or completely dark (not being illuminated by some or allof the pixels). With point-like or line-like light sources, care must betaken to provide some spreading or divergence of the light sources invertical and horizontal directions. Such an arrangement is shown inFIGS. 3. and 14., where a holographic diffuser 30 is positioned beforethe screen 20. The diffuser used in the apparatus of the invention is asingle diffracting or refractive optical element, or a combination ofmultiple elements. The spread or divergence angle δx caused by thediffuser in horizontal direction is at least as large as the angle γbetween two neighbouring light beams, but not larger than 2·γ, while thespread or divergence angle δy in vertical direction is larger than thehorizontal divergence, max. 180°. If the divergence angle δx issubstantially greater than the angle γ, e. g. 2·γ, the depth of fieldwill deteriorate substantially, because neighbouring light beams willoverlap too much, resulting in a flickering effect in the perceivedimage.

[0092] A further embodiment is shown in FIG. 4, where S light sourcesarranged in vertical and adjacent strips are shown, instead ofpoint-like sources. As seen in FIG. 4., the divergence anglesδi−1,δi,δi+1 of the adjacent light sources Si-1, Si, Si+1 are alsoadjacent, i. e. the viewer will perceive a continuous, uninterruptedimage. Only the horizontal divergence angle δx is shown in FIGS. 3 and4, while in FIG. 14 the horizontal divergence angle δx and the verticaldivergence angle δy are shown simultaneously, where δx<<δy<180°.

[0093] Several possible embodiments of the light sources schematicallyshown in FIG. 4 are illustrated in FIGS. 5,6, 7 and 9. According to FIG.5, the light emitting surface 10 is made of a ground glass sheet 40 orof a similar material, providing proper diffuse light emissionproperties into a large exit angle β. Behind the glass sheet 40 thereare S light sources positioned equidistantly from each other, and in adefinite distance behind the glass sheet 40. The light sources has angleindependent or time-constant angle dependent radiation characteristics,i. e. their light intensity may not be modulated differently indifferent exit angles. With other words, modulation or switching of thelight sources will result in the same modulation or switching of theemitted light in all exit directions (exit angles).

[0094] There are separating plates 50 between the light sources, alsoequidistant from the neighbouring light sources. The position of theseparating plates and the light sources define the exit angle β. In theembodiment of FIG. 5 there is no overlap between the light beamsentering the glass sheet 40. This may cause non-uniform illumination ofthe image. Therefore, to compensate this effect, overlapping regions maybe created in the glass sheet 40 by retracting the separating platesslightly from the glass sheet 40. This latter arrangement is illustratedin FIG. 6.

[0095] While in FIGS. 5 and 6 the light emitting surface 10 is shownfrom above, FIG. 7 shows a part of the light emitting surface 10 fromthe front. The structure formed of the separating plates 50 and thelight sources S1, S2, S3 is repeated in the same geometry, verticallyand horizontally. It is advantageous to repeat the light sources beloweach other, in order to provide a uniform illumination of the groundglass sheet 40.

[0096] With an other embodiment, the light sources below each other maybe differently coloured light sources, radiating in the basic R-G-Bcolours, and repeated in a regular pattern, typically realised as colourLEDs. Such an arrangement is shown in FIG. 9.

[0097] It is foreseen that groups are created from the light sources, sothat neighbouring light sources in a number according to the number ofviewing directions constitute one group. The switching on of the lightsources are performed so that only one light source within a group isswitched on at one time, preferably those light sources that are in thesame position in the different groups, while the pixels P of the screen20 is controlled according to the viewing directions defined by therelevant pixel and the light source currently being switched on, and theimage to be shown in each of the defined viewing directions. Thereafter,the light source or the column of the light sources is switched off, andsimultaneously in each group, the light source in the next positionwithin the group is switched on. At the same time, the controlling ofthe pixels also change corresponding to the image in the various viewingdirections. With other words, the light sources S are addressedcyclically. The control signals within one addressing cycle for thelight sources S1-S3 is schematically illustrated in FIG. 8.

[0098] With the arrangement of FIG. 11, where the light emitting surface10 is at a maximal distance Dmax from the screen 20, the light sourcesS30 and S60 must be switched simultaneously in order to illuminate thescreen 20 completely. Switching S30 and S60 off, the next light sourcesS1 and S31 are switched on, after that S2 and S32 etc.

[0099] With the arrangement of FIG. 12, where the light emitting surface10 is in a distance from the screen 20, which is half of the maximaldistance Dmax, the light sources S30, S60 and S90 are switched on andoff simultaneously. After that, S1, S31, S61 is switched on and off,than S2, S32 and S62, etc.

[0100] With the arrangement of FIG. 13, where the light emitting surface10 is in a distance from the screen 20, which is a quarter of themaximal distance Dmax, the light sources S30, S60, S90 and S 120 areswitched on and off simultaneously. After that, S1, S31, S61, S91 isswitched on and off, than S2, S32, S62 and S92, etc.

[0101] The pixels P of the screen 20 are always controlled correspondingto the direction of the exiting light beam and the position of the pixelthrough which the light beam is emitted. With this solution theresolution of the LCD screen will not decrease, and the controllingfrequency increases only proportionally with the number of viewingdirections.

[0102] In order to display colour images, several solutions areforeseen. With a first solution, the colour of the light sources ischanged periodically according to the three basic colours (timesequential colour control), while the pixels P of the screen 20 arecontrolled according to the fraction of the relevant colour component inthe image point represented by the respective pixel. The cyclicaddressing of the colour light sources R1-R3, G1-G3, B1-B3 of FIG. 9 isschematically illustrated in FIG. 10. With a second solution, the colourimages are displayed with white light sources and a coloured screen.

[0103] The controlling of the light sources S and the pixels P isperformed cyclically (periodically), with a frame frequency of at least20 Hz, preferably at least 25 Hz. During one frame controlling cycle,one image is projected in each viewing directions, so that in one cycleeach light source is switched on and off once, while each pixel iscontrolled once for every viewing direction, that is thirty times withina controlling cycle. Because the light sources are grouped together innumbers corresponding to the number of viewing directions, within acontrolling cycle each light source is activated once, so within a imageframe cycle the information corresponding to each viewing directions ofa still frame is presented. However, it must be noted that the actualimage information of a complete real image in any given viewingdirection never appears on the screen 20 together. Instead, thedifferent pixels of the screen 20 will show the different parts of aview of a still frame distributed within the image frame cycle. From theabove it is apparent that with this arrangement the controllingfrequency of the screen 20 is independent of the size of the screen orof any other geometrical relation. This screen controlling frequency (orpixel controlling frequency) is a product of the frame frequency and thenumber of the viewing directions only. Selecting a 25 Hz frame frequencyand Ip=30, the screen controlling frequency of the LCD screen will be750 Hz. Therewith the screen controlling frequency need not be greaterthan with the known prior art systems. For this purpose an LCD displaydeveloped by Boulder Nonlinear Systems, Inc. may be applied. This LCDdisplay is capable of delivering a 4000 frame/s frequency.

[0104] In FIG. 14, in an arrangement illustrated in a schematicperspective view, the point-like S1 . . . Sn light sources arepositioned in a horizontal line behind the screen 20, according to thegeometry discussed earlier. Of course, one horizontal line of lightsources allow only one vertical view, i. e. the 3D image created lacksthe vertical parallax information. If the vertical parallax is omitted,it is advantageous to provide an optical element before the screen 20,which spreads the incident light beams with a smaller horizontaldivergence angle δx and with a larger vertical divergence angle δy. Thiswill result in that the emitted light beams will be visible, practicallyindependently of the height of the viewer's eyes, and the visible imagewill not be confined to a vertically small horizontal region. Therefore,there is a diffuser 30 positioned before the screen 20. The opticaldeflecting function of this diffuser 30 may be realised with holographicoptical elements, or cylindrical optical elements having differentvertical and horizontal focus.

[0105]FIGS. 15 and 16 illustrates the application of extended sources(non-point sources), which ensure the necessary vertical and horizontaldivergence angles δx and δy without further deflecting optics.

[0106] In the arrangement shown in FIG. 15, the light sources S11, . . ., Smn are realised as uniformly illuminated, adjacent rectangular fieldsarranged in a matrix, and thereby allow the presentation of 3D imageshaving true perspective views both in vertical and horizontaldirections. An other solution is shown in FIG. 16, without verticalparallax, but with a relatively large vertical divergence angle δy. Herethe light sources S1 . . . Sn are constituted by vertical, uniformlyilluminated adjacent illuminating strips. Such strips may also besubstituted with the matrix arrangement of FIG. 15, where the columns ofthe light sources are controlled in a parallel manner.

[0107] It must be emphasised that the screen 20 may be a reflectivescreen as well. In this case, the light beam emitted from the lightsources S1-Sn will be reflected back towards the same side of the screen20 where the light sources are situated. This arrangement is illustratedwith FIGS. 17 and 18. In order to allow the viewers see the screen 20,the light emitting surface 10 is situated so that the light beamsemitted from the light sources S1-Sn will not be perpendicular to thescreen 20 in the Y-Z plane, but at an oblique angle. In this manner theobservation of the reflected beams will not be obstructed by the lightemitting surface 10, and the viewers will be able to watch the screen 20undisturbed. In this way the screen 20 may be fixed on a wall, while thelight emitting surface 10 may be formed as an overhead projector.

[0108] The inventive concept is equally applicable when the projectedimages, more precisely, the light beams creating the perceived images,are not modulated with the image information on the light emittingscreen 20, but on the light emitting surface 10. This is illustrated inFIG. 19, where the basic structure of a further apparatus for thepresentation of three-dimensional images is shown. This apparatus alsocomprises a light emitting surface 10, which is provided with lightsources S. As before, the light sources S themselves have angleindependent or time-constant angle dependent radiation characteristics.These light sources may be realised as individually addressable LED-s26, or as an integrated LED display.

[0109] In order to avoid crosstalk between the horizontal lines of lightsources and shutter pixels in the neighbouring horizontal lines, theradiation characteristic of the LED-s 26 should have little or novertical divergence, and a relatively large horizontal divergence, asshown in FIG. 22. This ensures that the light sources illuminate onlythe associated shutter pixels arranged in a horizontal direction, namelythose shutter pixels only that are in the same line as the respectivelight sources. For this purpose, a physical separation may be providedbetween the neighbouring horizontal lines of the pixels and lightsources, in the form of opaque horizontal plates extending between thesurface 10 and the screen 20. Alternatively, the radiationcharacteristic shown in FIG. 22 may be achieved with appropriate beamshaping optical elements (not shown) applied on the LEDs 26.

[0110] There is also a screen 20 before the light emitting surface 10,and the screen 20 comprises cyclically addressable shutter pixels 25.The shutter pixels 25 have a controllable light transmission orreflection. The pixels of the screen 20 are here termed as “shutter”pixels because they are either transmitting (or reflecting) the incidentlight essentially without intensity modulation, or completely block thelight. It is also foreseen that the shutter pixels are able to modulatethe transmitted light.

[0111] In the embodiment shown in FIG. 19, the shutter pixels 25 operatein a transmission mode. The light of the light sources S propagatesessentially without changing direction between the light sources S andthe shutter pixels 25, and through the shutter pixels 25. However, asshown FIGS. 17 and 18, the screen 20 may operate in a reflection mode aswell.

[0112] The resolution of the images displayed by the apparatus isdetermined by the resolution (density) of the shutter pixels, in thesense that the displayed 3D image may have as many image points in aviewing direction as there are shutter pixels on the screen 20. Becauseas a person viewing the screen 20 can only receive light from theapparatus which is emerging from a shutter pixel 25, hence theresolution of the perceived image is determined by the resolution of thescreen 20. At the same time, the angle resolution of the apparatus,which defines the field of depth of the 3D view, is determined by thedensity of the light sources S. As will be shown below, there is atradeoff between selecting a high angle resolution and high displayoperating frequency, or having a lower angle resolution and therebylowering the display operating frequency as well.

[0113] Each light source S illuminates several shutter pixels 25, andone shutter pixel is illuminated by several light sources within acycle. In FIG. 19 it is seen that the light of the light sources Sn-4−Snpass through a single shutter pixel P_(m−2), which is in the “on” state,i. e. it is transmissive. The neighbouring shutter pixels in the samehorizontal line are in the “off” or blocking state.

[0114] A single shutter pixel is illuminated at one time by a group oflight sources S, e. g. the pixel Pm-2 in FIG. 19 is illuminated by thelight sources Sn-4, Sn-3, . . . Sn. Similarly, in FIG. 21A it is seenthat the light of the light sources S3,S4,S5 pass through the singleshutter pixel P_(1+k). At the same time, the light of one light sourcewithin that group is transmitted through that single shutter pixel only,because the neighbouring shutter pixels are in an off state. The lightsources S and the shutter pixels P are modulated so that in each imagecycle each shutter pixel is transmitting light at least once in eachviewing direction, i. e. a light beam will be emitted from each shutterpixel towards each viewing direction in each image cycle.

[0115] A composed image is generated on the light emitting surface 10 bycontrolling the light sources S. This composed image does not correspondto any real image or real view, i.e. an image that is actually seen bythe viewer from any direction. The light sources S creating thiscomposed image are modulated according to those image details associatedto an image, which image details should be seen from the differentviewing directions at the location of the single open shutter pixel.

[0116] As the shutter pixels are turned on and off cyclically, e. g.arranged in columns 27 shown in FIG. 19, the images projected in thedifferent directions are obtained by cyclically transmitting lightthrough the shutter pixels. The horizontal distance between the columns27 are chosen so that light emitted from any of the light sources S mayreach only one single “open” shutter pixel, so that the given lightsource S may be modulated according to a single viewing direction of theprojected image, the viewing direction being determined by the relativeposition of the light source and the open shutter pixel.

[0117] The light sources S of the light emitting surface 10 and theshutter pixels 25 of the screen 20 are controlled by an appropriate acontrol unit (not shown).

[0118] The principle of the cyclical control of the shutter pixels andthe light sources is demonstrated in FIGS. 20 and 21A-21E. As it is seenin FIG. 20, all light sources S1-Sn on the light emitting surface 10have the same light emitting characteristic, and the light sources areable to emit light in an exit angle β, similarly to the light sourcesshown in FIG. 2. In FIG. 20, all shutter pixels P1-Pm are in atransmitting (on) state. It is seen that each shutter pixel isilluminated by a certain fixed number of light sources. As explainedabove, the number of light sources illuminating a shutter pixel isdependent on the distance of the exit angle β, the distance between thelight sources, and the distance between the light emitting surface 10and the screen 20. In the schematic, illustrative arrangement of FIG.20, each shutter pixel is illuminated by three neighbouring lightsources, e.g. the pixels P3 and P4 are illuminated by the light sourcesS1,S2 and S3. At the same time, a single light source is able toilluminate six neighbouring shutter pixels, e. g. the light source S3illuminates the pixels P1-P6.

[0119] FIGS. 21A-E show that within a viewing cycle, practically withinan image frame of approx. {fraction (1/20)}-{fraction (1/30)} sduration, each shutter pixel—being illuminated by three light sources—isturned on. Since one light source illuminates six shutter pixels, butthe modulation of a single light source can be done according to asingle view seen from a single pixel only, the light sources must bemodulated once for each illuminated pixel. This means that the screen 20must be also modulated with a speed of 6×30 Hz in the shown embodiment,i. e. the image frame is further divided into six time slots orintervals, denoted by t1-t6.

[0120]FIG. 21A illustrates that in the first time slot t1 within oneimage frame, the pixels P₁ and P_(1+k) (and further P_(1+2k), P_(1+3k),. . . etc., these are not shown in FIG. 20) are turned on. The value ofk is selected to ensure that the light of a light source is nottransmitted through more than one open shutter pixel. Obviously, thevalue of k is equal to the number of the shutter pixels illuminated by asingle light source, i. e. in the shown embodiment k=6. The number ofshutter pixels to be switched in a cycle may be also calculated asIp*Xs/Xp, where Ip is the number of light emitting directions from ashutter pixel. As will be shown below, this number also determines thespeed of the shutter pixel screen 20.

[0121] In the next time slot t2, the next shutter pixels P₂ and P_(2+k)(and further P_(2+2k), P_(2+3k), . . . etc,) are turned on, as shown inFIG. 21B. Thereafter, in the next time slot t3, the next shutter pixelsP₃ and P_(3+k) (and further P_(3+2k), P_(3+3k), . . . etc,) are turnedon, as shown in FIG. 21C. FIG. 21D illustrate the situation in the timeslot t4, and FIG. 21E illustrate the situation in the final time slott6, within one image frame.

[0122] As it may be understood from the figures, within one image frameall shutter pixels are opened once, for the duration of a time slot,being a fraction of an image frame. At the same time, light modulated bydifferent light sources is emitted from different viewing directionsfrom the shutter pixels. Modulating the light according to theappropriate viewing directions, different images may be projectedtowards the different viewing directions, i. e. three-dimensional imagesmay be obtained. Obviously, this requires that the light sources S aremodulated with the same frequency as the shutter pixels. With otherwords, the light emitting surface must be realised as a fast display,preferably as a LED-display or OLED display.

[0123] From FIG. 20 it is apparent that the distance between the centresof the light sources S is larger than the distance between the centresof the shutter pixels P. As explained above, the distance D between thelight sources and the shutter pixels is selected so that more shutterpixels are illuminated by one light source within a cycle (one imageframe) as there are light sources illuminating a single shutter pixel.

[0124] From the above it follows that the distance between the lightsources S may be rather large, which may be advantageous with some typesof light sources, e. g. if the light emitting surface 10 is constructedfrom individual LEDs, in order to achieve high brightness. This may bealso formulated so that resolution of the light emitting surface 10 canbe lower than the resolution of the screen 20. However, this lowerresolution must be compensated by the higher operating frequency of boththe screen 20 and the light sources of the screen 20. It can be shownthat the cycle frequency f_(c) of both the screen 20 and the surface 10(i. e. the light sources S) may be calculated as follows:f_(c)=f_(i)×Ip×k₁,where

[0125] f_(i) is the frame frequency of the video image to be displayed,typically 20-30 Hz,

[0126] Ip is the number of different viewing directions obtained withthe display, i. e. the number light emitting directions from a singleshutter pixel, and

[0127] k_(i) is a constant calculated as the ratio between the distancesof the light sources and the shutter pixels (Xs/Xp).

[0128] With other words, if the resolution of the LED screen 10 is lessthan the resolution of the screen 20, this must be compensated withhigher operating frequency, in order to produce the necessary number ofdifferent light beams emerging from the shutter pixels. LED screens withhigh operating frequency are feasible, while the realisation of thescreen 20 may be done with a high-speed LCD display. However, thecontrol of the screen 20 is made advantageously easier, because onlyon-off modulation is needed, instead of a grey-scale modulation.Therefore, the screen 20 may be realised not only as a screen with apixel structure, but also as a screen with moving shutter slits.

[0129] On the other hand, the light efficiency of the system alsodecreases, because only 1/k-th part of the light of the light sources isutilised. Therefore, it is generally less efficient to modulate thelight sources. Instead, the modulation of the pixels is preferred, aswith the embodiment shown with reference to FIGS. 2-18.

[0130] The screen 20 is also equipped with a diffractive screen, with asimilar function and structure as the holographic diffuser 30 shown inFIGS. 3. and 14 (not shown in FIG. 19). Also, it is foreseen that thefeatures of the advantageous embodiments of the light sources and theimage pixels explained with reference to FIGS. 2-18 are equally suitablefor the apparatus shown in FIG. 19, where applicable.

1. Method for the presentation of three-dimensional images, where lightbeams with appropriate intensity and optionally with appropriate colourare projected in different viewing directions, thereby creating athree-dimensional image, wherein a light emitting surface comprisingseparately controllable light sources with angle independent ortime-constant angle dependent radiation characteristics is positionedbehind a screen, the screen comprising image pixels with a controllablelight transmission or reflection, where the light beams emitted fromdifferent light sources illuminate the individual image pixels fromdifferent directions, and further the direction of the light beamsemitted from the individual image pixels are determined by the directionof the light beams that are emitted by the light sources and propagatingbetween the light sources and the image pixels substantially withoutchanging direction, characterised in that d, the distance between thelight sources are selected larger than the distance between the imagepixels, and e, the light sources are positioned so much away from theimage pixels so that the number of image pixels illuminated by one lightsource is greater than the number of light sources illuminating oneimage pixel.
 2. The method according to claim 1, characterised in thatthe ratio of the number of image pixels illuminated by one light sourceto the number of light sources illuminating an image pixel equals theratio of the distance between the centres of the light sources to thedistance between the centres of the image pixels.
 3. The methodaccording to claim 1 or 2, characterised in that the light beams emittedfrom the individual image pixels are spread in horizontal and verticaldirection with a divergence angle necessary for the uniform illuminationof the field of view, from which field of view a three-dimensional imagemay be perceived.
 4. The method according to claim 3, characterised inthat the horizontal divergence angle is at least as large as the anglebetween two neighbouring viewing directions.
 5. The method according toclaim 3, characterised in that the image pixels are illuminated by lightsources which are adjacent to each other and having uniform surfaceillumination, and the size of the light sources are determined by thehorizontal and vertical distance between them.
 6. The method accordingto claim 3, characterised in that the light sources are point-like lightsources, and the different vertical and horizontal spread (divergence)of the light beams emitted from the individual image pixels is achievedwith an appropriate diffuser.
 7. The method according to any one ofclaims 1 to 6, characterised in that the image pixels and the lightsources are controlled in a manner that a, the light sources areswitched on and off individually or in groups so that an image pixel isilluminated at one time by not more than one light source, and at thesame time each image pixel is illuminated by a light source, b, thelight sources are switched on and off periodically or cyclically oneafter the other so that in each period or cycle each image pixel isilluminated at least once in each viewing direction, and in themeanwhile c, the images projected in the different directions areobtained by the appropriate intensity and/or colour modulation of thelight transmitted through or reflected from the image pixels,
 8. Themethod according to claim 3, characterised in that images withoutvertical parallax are displayed, and the different horizontal andvertical spread (divergence) of the light beams emitted from the imagepixels are obtained by adjacent vertical light source strips.
 9. Themethod according to any one of claims 7 to 9, characterised in thatgroups are created from the illuminating light sources, where as manyneighbouring light sources constitute a group as there are viewingdirections, and the switching of the light sources are performed in amanner so that at one time only one light source is switched on fromeach group, preferably the light sources in the similar position, whilethose image pixels, which correspond to a selected viewing direction,are controlled with the appropriate image information corresponding tothe selected viewing direction, and thereafter the light sourcescurrent1y on are switched off, and substantially simultaneously in eachgroup the light sources in the next position are switched on, andsimultaneously the control of the image pixels is changed correspondingto the next viewing direction.
 10. The method according to any one ofthe claims 7 to 9, characterised in that for presentation of colourimages the colour of the light sources are changed during the switchedon state, according to the three basic colours, while the image pixelsof the screen comprising the controllable image pixels are controlledaccording to the colour ratio of the corresponding colour component. 11.The method according to any one of the claims 7 to 9, characterised inthat for presentation of colour images white light sources and colouredscreen is used.
 12. The method according to any one of the claims 7 to9, characterised in that one control period or control cycle is notlonger than {fraction (1/20)} s, preferably {fraction (1/25)} s, andwhere within one control cycle each light source is activated once,while within one control cycle each image pixel is controlled once ineach viewing directions, within one control cycle as many times as thereare viewing directions.
 13. The method according to any one of theclaims 1 to 6, characterised in that the image pixels are realised aslight shutter pixels, and a composed image containing parts of acomplete image is generated on the light emitting surface by modulatingthe light intensity emitted by the light sources, and further theshutter pixels and the light sources are controlled in a manner that a,a single shutter pixel is illuminated at one time by a group of lightsources, each of the light sources in that group corresponding to aviewing direction, and at the same time the light of one light sourcewithin that group is transmitted through a single shutter pixel only, b,the shutter pixels and the light sources are modulated so that in eachimage cycle each shutter pixel is transmitting or reflecting light atleast once in each viewing direction, and c, the complete imagesprojected in the different directions are obtained by cyclicallytransmitting light through the shutter pixels.
 14. Apparatus for thepresentation of three-dimensional images, particularly for theperforming of the method according to claim 1, the apparatus comprisinga, a light emitting surface provided with separately controllable lightsources with angle independent or time-constant angle dependentradiation characteristics, and b, a screen comprising image pixels witha controllable light transmission or reflection and positioned beforethe light emitting surface, where c, the light of the light sourcespropagates essentially without changing direction between the lightsources and the image pixels, and through the image pixels or beingreflected from the image pixels, and where each light source illuminatesseveral image pixels, and one image pixel is illuminated by severallight sources, characterised in that d, the distance between the centresof the light sources is larger than the distance between the centres ofthe image pixels, and e, the distance between the light sources and theimage pixels is selected so that more image pixels are illuminated byone light source as there are light sources illuminating a single imagepixel.
 15. The apparatus according to claim 14, characterised in thatthe light sources on the light emitting surface are so far from theimage pixels, so that the ratio of the number of pixels illuminated byone light source to the number of the light sources illuminating asingle pixel is substantially equal to the ratio of the distance betweenthe light sources to the distance between the image pixels.
 16. Theapparatus according to claim 14 or 15, characterised in that the screencomprising the controllable image pixels further comprises a diffuserfor providing different spread (divergence) of the light beams emittedfrom the individual image pixels in vertical and horizontal directions.17. The apparatus according to claim 16, characterised in that thescreen comprises a holographic layer or lenticular lens matrix.
 18. Theapparatus according to any one of the claims 14 to 17, characterised inthat light sources are realised as LEDs, particularly as LEDs of a LEDarray, LED display or OLED display.
 19. The apparatus according to anyone of the claims 14 to 18, characterised in that the screen comprisingthe controllable image pixels is constituted by an LCD display or another LCD panel.
 20. The apparatus according to any one of the claims 14to 19, characterised in that the light sources are formed as lightsources with a predetermined vertical and horizontal size, the sizedetermined for providing means for spreading of the light beams emittedfrom the individual image pixels in vertical and horizontal directions.21. The apparatus according to any one of claims 14 to 20, characterisedin that the light sources are formed as vertical light source stripspositioned adjacent to each, in order to provide different spread of thelight beams emitted from the individual image pixels in vertical andhorizontal directions.
 22. The apparatus according to any one of theclaims 14 to 19, characterised in that the light sources aresubstantially point sources.
 23. The apparatus according to any one ofthe claims 14 to 19, characterised in that the light sources arediscrete light sources separated by dividing plates, and positionedbehind a diffusing surface.
 24. The apparatus according to claim 23,characterised in that the diffusing surface is made of ground glass. 25.The apparatus according to claim 24, characterised in that the lightsources and the dividing plates separating the light sources are at adistance behind the ground glass, in order to ensure space for theoverlapping of the light cones emitted from the light sources.
 26. Theapparatus according to any one of the claims 15 to 18, characterised incomprising multiple light sources at an equal distance below each otherbehind the diffusing surface.
 27. The apparatus according to any one ofthe claims 14 to 26, characterised in that the light sources positionedbelow each other are light sources for the irradiation of basic colourssuitable for the presentation of coloured images, and where the basiccolours are repeated regularly.
 28. The apparatus according to any oneof the claims 14 to 19, characterised in that the image pixels of thescreen are cyclically addressable light shutter pixels, where each lightsource illuminates several shutter pixels, and one shutter pixel isilluminated by several light sources within a cycle.
 29. The apparatusaccording to claim 28, characterised in that the light sources has aradiation characteristic for illuminating multiple shutter pixelsarranged in a horizontal direction.